Preparation of drilling muds



. sets or gels.

- the proper gel rate and gel strength.

when such a drilling fluid is circulated through- -a well bore,. it has sumciently high viscosity Patented Feb. 6, 1945 PREPARATION OF DRILLING MUDS Allen D. Garrison, Houston, Tex., assignor, by memo assignments, to The Texas Company, New York, N. Y., a corporation of Delaware No Drawing. Application August 25, 1937,

i Serial NIL. 160,820

Claims. (01. 252-85) This invention relates to drilling muds and more particularly to the preparation and control of drilling muds employed in the drilling of wells.

More specifically, my invention relates to a method of controlling the colloidal and physical properties of a' drilling mud so as to maintain it in the most desirable condition for use and it becomes necessary to discontinue circulation I for a period of time.

which comprises adding sodium triphosphate to the drilling mud.

Drilling muds are used in the drilling of wells employed for tapping underground collections of oil, gas, brines or water. These muds fulfill various functions. the most important of which are to assist-in the removal of cuttings from the well, to seal of! formations of gas, oil and water which may be encountered at various levels, and tolubricate the drilling tool and the drill pipe which carry the tools.-

Drilling muds are essentially mixtures of finely divided solids, such as clay, with water, usualperiods of discontinued circulation.

' is particularly dangerous in those cases where- 1y so compounded that they weigh from eight to twelve pounds per gallon. Whenever it is found necessary to increase the specific gravity of a particular mud it is customary to add thereto finely divided materials which have a high specific gravity, such, for example, as iron oxide, barytes, litharge and the like.

The solid phase of a drilling mud consists of colloidal and non-colloidal particles. It is the colloidal particles which are responsible for the colloidal character of the drilling mud, and due to their presence drilling muds. are essentially colloidal dispersions. An ideal drilling mud is a thixotropic colloidal system, that .is to say, a

fluid, which on agitation, as bypumping or otherwise, has a relatively low viscosity and is freefibwingjbut when agitation .is stopped gradually This gelling action is sumciently slow to permit the cuttings to settle two or three feet before the gel structure which is developing during this time is strong enough to support them. For the purpose of convenience I intend that the term thixotropic drilling mud connote a drilling fiuid having proper viscosity and In use to carry the cuttings and sand from the bottom of the hole to the surface, and it has a sufiieiently slow gelling rate to allow the cuttings and sand to settle in a settling pit.. On stand ing in a quiescent state it develops sufilcient gel strength to prevent the settling of the cuttings,

The use of a drilling mud which is non-thixotropic i attended by many disadvantages, allof which are well known to those skilled in the art of drilling wells. A non-.thixotropic drilling mud is one which either develops no gel at all, or which flocculates rapidly enough to remain in a plastic-state even while in motion. The former condition results-in the settling ofsuspended solids to the bottom'of the bore hole during On the other hand, a drilling fluid which gels too rapid- 1y is difllcult to maintain free of cuttings and sand. Such a drilling mud or adequate viscosity at normal circulating rate easily becomes gas cut because of the recirculation of gas bubbles trapped by the rapid-forming gel or flocks. This the bore hole traverses or encounters high gas pressures, because the gas cutting of the mud may so reduce the hydrostatic head of the drilling mud in the bore hole as to result in the blowing out of the well.

Drilling muds are generally prepared by suspending in water, clays which will yield thixo- Such clays contain intropic colloidal systems. varying amount complex colloidal alumino-silicates which are essentially acids whose anion is amicell of the general formula,

X(A12O3)Y(SiO2)Z(I-I2O) where X is approximately 1, Y is approximately 3, and Z may vary over, wide values. In the interest of simplicity, this anion will be termed hereinafter as clay and the compounds formed by its combination with various cationswill be termed clays of cations; so, for example, the

hydrogen compound will be termed hydrogen clay, the sodium compounds will be termed sodium clays, while the calcium compounds will be called calcium clays,

It has been observed that dispersions in water of either acid clays or multivalent ion clays tend' to gel rapidly, and are very sensitive to coagulation by dissolved salts o impurities. Obviously such types of dispersions are undesirable as drill-' ing fluids since small amounts of soluble salts in the formations being drilled cause either too high a gelling rate or actual flocculation. The alkali metal clays are more readily rendered thixotropic and require larger amounts of salts and impurities to cause rapid gelling and flocculation.

sand or barytes. e c, in the well boreitseli when Although drilling fluids having satisfactory thi rotropic properties may be prepared by the use of suitable clays, these desirable properties are lost in varying degrees during the penetration of certain shales, clays and water-bearing formations. This deterioration of thixotropic drilling muds may involve the conversion of monovalent ion clay into an acid clay or a multivalent ion clay. The former occurs when the thixotropic drilling mud encounters acid state; the latter, which is the more common, occurs when the drilling mud encountersstrata'of calcium and magnesium clays or soluble compounds. Under such circumstances a phenomenon known as base exchange occurs whereby the monovalent' ion clays are converted into multivalenii ion clays, and are thereby rendered more sensitive to flocculating impurities.

Flocculation or coagulation of any of the types of clays by fiocculating materials such as salt encountered during drilling and the rapid accumulation of colloidal matter from shalcs or clays penetrated increase both the viscosity of the drilling mud and its gel-strength to undesirably high values. Dilution of the mud with water, which is frequently employed to remedy this condition, is particularly undesirable if high gas pressures are encountered, since the specific gravity of the fluid is thereby lowered and more gas permitted to enter the well core.

I have discovered that sodium triphosphate not I only possesses the property of reducing the viscosity of drilling muds, but also possesses the unusual property of reducing the gel strengths of drilling muds to which it is added in small amounts to the pointat which sand and cuttings are substantially completely settled out of the drilling muds. Tests carried out by me with a Tun: I

Viscosity in Grams of sodium trlphosphato per 100 cc. of

d d 1 centipoises rilling mu TAsu: II

Efiect of sodium hexametaphosphate on the viscosity ofa drilling mud having an original viscosity of 45 centipoises' Grams of sodium hcxametaphosuhate per Viscosity in 100 cc. of drilling mud centipoiscs the selective settling of sand and cuttings from mixture of caustic soda and quebracho, with sodium hexametaphosphate, sodium thiotetraphosphate, di-sodium hydrogen phosphate and sosodium triphosphate was used for reducing the viscosity of a drilling mud. I also offer for purposes of comparison the tests obtained ona sample of the same type of drilling mud treated with given amounts of sodium hexametaphosphate.

The sodium triphosphate employed in the experiments was prepared by fusing together a mixture of anhydrous sodium pyrophosphate and 'sodium metaphosphate at a red heat and then quickly cooling the melt by pouring the same in a thin layer upon an iron plate. The reaction between the sodium pyrophosphate and the sodium metaphosphatemay be designated as follows:

N$4P207+N$PQ3=N85PSO10 The arming mud used in the followingeirperiments consisted of a suspension in water of a shale obtained in the Manvel oil field at Manvel.

Texas. This mud had a viscosity of 45 centipoises measured at avelocity of 600 R. P. M. in

- the Stormer visccsimeter. The reagents, sodium triphosphate and sodium hexametaphosphate.

were added to samples of this drilling mud in amounts which are indicated in the followingtables 'as grams per 'one hundred cc. of drilling mud. .I'he viscosities appearing in the tables are the Stunner 'viscositics taken at 600 R. P. M. i

dium triphosphate, showed that sodium triphosdrilling muds.

The amounts of sodium triphosphate necessary to practice my invention depend upon numerous factors, such as the type of drilling mud to be treated, the amount of improvement or the degree of protection thatis desired in the drilling Those.

mud, as well as the conditions of use. skilled in the art will appreciate that in view of the foregoing it is impossible to set any speciflc limitations as to the amounts of the reagent. I have found, however, that an amount within the range 0.001% to 0.1% by weight of the reagent will produce the desired result.

My invention may be carried out in several different ways. For example. I may prepare a. drilling mud by incorporating the desired amount of sodium trlphosphate directly in a suspension of clay in water, or I may add the necessary amount of this compound to a drilling mud which is flocculated in order to reduce its viscosity to a value at which the drilling mud can be effectively' used. I also contemplate the continuous addition of a. solution of sodium triphosphate to a drilling mud during use to prevent any substantlal change in its colloidal and physical characteristics.

It is intended that the word clay" as used herein shall include bentonite-clays containing appreciable quantities of bentonlte, as well as those clays which. display the properties of deflocculating in water. Ialso intend that the term 1 finely divided solids" shall include both clays and all other finely divided water-insoluble solids. including materials such as iron oxide, barytes, litharge and the like, or any mixtures thereof.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made; without departing from the spirit and scope thereof, and onlysuch limitations should gedimposed as are indicated in' the appended I claim: 1. A mud laden drilling fluid containing a small percentage of sodium triphosphate. I

2. In the art of drilling wells by the employment of a drilling fluid, the process comprising 5 adding to the drilling fluid a. small percentage of sodium triphosphate.

3. A drilling mudcomprising a. finely-divided solid, water and sodium triphopshete.

4. A drilling mud comprising clay, water and 10 from 0.001% to 0.1% by weight 0! sodium triphosphate.

5. In the'art of drilling and controlling wells in which a. drilling mud is circulated in the bore hole. the process of reducing the viscosity of the mud comprising treating the mud with from 0.001% to 0.1% by weight of sodium triphosplum.

ALLEN D. GARRISON. 

